A human corpse cannot respond to a living human being, but a living human being can respond to a corpse. For example, a living human can imitate a corpse, can show to others that a corpse cannot respond to questions put to it, and so on.
A living human may address the corpse of a loved one in speech and speak of the suffering and grief of personal loss. Is the person speaking to the corpse itself? No. But, the living human animates the corpse with personal memories, sensations and emotions that instead replace the corpse with the living, dynamic person that once was, and give the spoken words their point. I don’t think this is an act of make-believe, since the memories are real.
‘Is the person speaking to the corpse itself?’ What does the child address when it talks to dolls? Is the child engaged in make-believe? My hunch is that toy-play is imitation: the child animates the toy with human behaviors and thoughts.